diff --git a/examples/lsystem_collection.scad b/examples/lsystem_collection.scad
index 8425e8e3..316da672 100644
--- a/examples/lsystem_collection.scad
+++ b/examples/lsystem_collection.scad
@@ -13,287 +13,287 @@ for(line = plant()) {
 
 function tree(n = 2, angle = 36, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F"],
+        axiom = "F",
+        rules = [
             ["F", "F[+FF][-FF]F[-F][+F]F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
 
 function plant(n = 4, angle = 25, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "X"],
+        axiom = "X",
+        rules = [
             ["X", "F+[[X]-X]-F[-FX]+X"],
             ["F", "FF"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
 
 function koch_curve(n = 4, angle = 60, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F"],
+        axiom = "F",
+        rules = [
             ["F", "F-F++F-F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
 
 function koch_curve_3(n = 3, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F-F-F-F"],
+        axiom = "F-F-F-F",
+        rules = [
             ["F", "FF-F+F-F-FF"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
 
 function koch_snowflake(n = 4, angle = 60, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F++F++F"],
+        axiom = "F++F++F",
+        rules = [
             ["F", "F-F++F-F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
 
 function koch_quadratic(n = 3, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F-F-F-F"],
+        axiom = "F-F-F-F",
+        rules = [
             ["F", "FF-F-F-F-F-F+F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
 
 function koch_quadratic_type1(n = 4, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F"],
+        axiom = "F",
+        rules = [
             ["F", "F-F+F+F-F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
 
 function koch_quadratic_type2(n = 4, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F"],
+        axiom = "F",
+        rules = [
             ["F", "F-F+F+FF-F-F+F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
 
 function koch_star(n = 4, angle = 60, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F++F++F"],
+        axiom = "F++F++F",
+        rules = [
             ["F", "F+F--F+F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start, "6789");   
+    lsystem2(axiom, rules, n, angle, leng, heading, start, "6789");   
 
 function dragon_curve(n = 10, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "FX"],
+        axiom = "FX",
+        rules = [
             ["X", "X+YF+"],
             ["Y", "-FX-Y"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);
+    lsystem2(axiom, rules, n, angle, leng, heading, start);
     
 function twin_dragon_curve(n = 8, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "FX+FX+"],
+        axiom = "FX+FX+",
+        rules = [
             ["X", "X+YF"],
             ["Y", "Y=FX-Y"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);    
+    lsystem2(axiom, rules, n, angle, leng, heading, start);    
     
 function hilbert_curve(n = 5, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "A"],
+        axiom = "A",
+        rules = [
             ["A", "-BF+AFA+FB-"],
             ["B", "+AF-BFB-FA+"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);    
+    lsystem2(axiom, rules, n, angle, leng, heading, start);    
 
 function moore_curve(n = 4, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "LFL+F+LFL"],
+        axiom = "LFL+F+LFL",
+        rules = [
             ["L", "-RF+LFL+FR-"],
             ["R", "+LF-RFR-FL+"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);      
+    lsystem2(axiom, rules, n, angle, leng, heading, start);      
 
 function peano_curve(n = 3, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "L"],
+        axiom = "L",
+        rules = [
             ["L", "LFRFL-F-RFLFR+F+LFRFL"],
             ["R", "RFLFR+F+LFRFL-F-RFLFR"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);       
+    lsystem2(axiom, rules, n, angle, leng, heading, start);       
 
 function gosper_curve(n = 4, angle = 60, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "A"],
+        axiom = "A",
+        rules = [
             ["A", "A-B--B+A++AA+B-"],
             ["B", "+A-BB--B-A++A+B"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start, "AB");    
+    lsystem2(axiom, rules, n, angle, leng, heading, start, "AB");    
 
 function gosper_star(n = 2, angle = 60, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "X-X-X-X-X-X"],
+        axiom = "X-X-X-X-X-X",
+        rules = [
             ["X", "FX+YF++YF-FX--FXFX-YF+"],
             ["Y", "-FX+YFYF++YF+FX--FX-FY"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);    
+    lsystem2(axiom, rules, n, angle, leng, heading, start);    
     
 function levy_c_curve(n = 8, angle = 45, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F"],
+        axiom = "F",
+        rules = [
             ["F", "+F--F+"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);       
+    lsystem2(axiom, rules, n, angle, leng, heading, start);       
 
 function island_curve(n = 2, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F-F-F-F"],
+        axiom = "F-F-F-F",
+        rules = [
             ["F", "F-M+FF-F-FF-FM-FF+M-FF+F+FF+FM+FFF"],
             ["M", "MMMMMM"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);  
+    lsystem2(axiom, rules, n, angle, leng, heading, start);  
     
 function sierpinski_triangle(n = 5, angle = 120, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F-G-G"],
+        axiom = "F-G-G",
+        rules = [
             ["F", "F-G+F+G-F"],
             ["G", "GG"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start, "FG");  
+    lsystem2(axiom, rules, n, angle, leng, heading, start, "FG");  
 
 function sierpinski_arrowhead(n = 6, angle = 60, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "XF"],
+        axiom = "XF",
+        rules = [
             ["X", "YF+XF+Y"],
             ["Y", "XF-YF-X"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);     
+    lsystem2(axiom, rules, n, angle, leng, heading, start);     
 
 function sierpinski_square(n = 8, angle = 45, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "L--F--L--F"],
+        axiom = "L--F--L--F",
+        rules = [
             ["L", "+R-F-R+"],
             ["R", "-L+F+L-"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);      
+    lsystem2(axiom, rules, n, angle, leng, heading, start);      
     
 function terdragon(n = 5, angle = 120, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F"],
+        axiom = "F",
+        rules = [
             ["F", "F+F-F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);    
+    lsystem2(axiom, rules, n, angle, leng, heading, start);    
 
 function pentadendrite(n = 2, angle = 72, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F-F-F-F-F"],
+        axiom = "F-F-F-F-F",
+        rules = [
             ["F", "F-F-F++F+F-F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);    
+    lsystem2(axiom, rules, n, angle, leng, heading, start);    
     
 function icy(n = 2, angle = 90, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F+F+F+F"],
+        axiom = "F+F+F+F",
+        rules = [
             ["F", "FF+F++F+F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);        
+    lsystem2(axiom, rules, n, angle, leng, heading, start);        
 
 function round_star(n = 3, angle = 77, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F"],
+        axiom = "F",
+        rules = [
             ["F", "F++F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);   
+    lsystem2(axiom, rules, n, angle, leng, heading, start);   
     
 function penrose_tiling(n = 2, angle = 36, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "[7]++[7]++[7]++[7]++[7]"],
+        axiom = "[7]++[7]++[7]++[7]++[7]",
+        rules = [
             ["6", "81++91----71[-81----61]++"],
             ["7", "+81--91[---61--71]+"],
             ["8", "-61++71[+++81++91]-"],
             ["9", "--81++++61[+91++++71]--71"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start, "6789");       
+    lsystem2(axiom, rules, n, angle, leng, heading, start, "6789");       
 
 function bush(n = 3, angle = 16, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "++++F"],
+        axiom = "++++F",
+        rules = [
             ["F", "FF-[-F+F+F]+[+F-F-F]"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);       
+    lsystem2(axiom, rules, n, angle, leng, heading, start);       
 
 function pentigree(n = 3, angle = 72, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F-F-F-F-F"],
+        axiom = "F-F-F-F-F",
+        rules = [
             ["F", "F-F++F+F-F-F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);         
+    lsystem2(axiom, rules, n, angle, leng, heading, start);         
 
 function penrose_snowflake(n = 3, angle = 18, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F----F----F----F----F"],
+        axiom = "F----F----F----F----F",
+        rules = [
             ["F", "F----F----F----------F++F----F"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);         
+    lsystem2(axiom, rules, n, angle, leng, heading, start);         
 
 function weed(n = 6, angle = 22.5, leng = 1, heading = 0, start = [0, 0]) = 
     let(
-        rule = [
-            ["S", "F"],
+        axiom = "F",
+        rules = [
             ["F", "FF-[XY]+[XY]"],
             ["X", "+FY"],
             ["Y", "-FX"]
         ]
     )
-    lsystem2(rule, n, angle, leng, heading, start);         
\ No newline at end of file
+    lsystem2(axiom, rules, n, angle, leng, heading, start);         
\ No newline at end of file
diff --git a/src/experimental/_impl/_lsystem2_impl.scad b/src/experimental/_impl/_lsystem2_impl.scad
index 3bea62e5..a008fc47 100644
--- a/src/experimental/_impl/_lsystem2_impl.scad
+++ b/src/experimental/_impl/_lsystem2_impl.scad
@@ -33,9 +33,9 @@ function _derive1(base, rules) = _join([
 function _derive(base, rules, n, i = 0) =
     i == n ? base : _derive(_derive1(base, rules), rules, n, i + 1);
     
-function _lsystem2_derive(rules, n, rules_pr) =
-    is_undef(rules_pr) ? _derive(rules[0][1], rules, n) : 
-    rand() <= rules_pr[0] ? _derive_p(rules[0][1], rules, rules_pr, n) : "";
+function _lsystem2_derive(axiom, rules, n, rules_pr) =
+    is_undef(rules_pr) ? _derive(axiom, rules, n) :
+                         _derive_p(axiom, rules, rules_pr, n);
 
 function _next_stack(t, code, stack) = 
     code == "[" ? concat([t], stack) :
diff --git a/src/experimental/lsystem2.scad b/src/experimental/lsystem2.scad
index 9cbc406b..3cee6129 100644
--- a/src/experimental/lsystem2.scad
+++ b/src/experimental/lsystem2.scad
@@ -1,9 +1,9 @@
 use <experimental/_impl/_lsystem2_impl.scad>;
 use <turtle/turtle2d.scad>;
 
-function lsystem2(rules, n, angle, leng = 1, heading = 0, start = [0, 0], forward_chars = "F", rules_pr) =
+function lsystem2(axiom, rules, n, angle, leng = 1, heading = 0, start = [0, 0], forward_chars = "F", rules_pr) =
     let(
-        derived = _lsystem2_derive(rules, n, rules_pr),
+        derived = _lsystem2_derive(axiom, rules, n, rules_pr),
         codes = forward_chars == "F" ? derived : _join([
             for(c = derived)
             let(idx = search(c, forward_chars))