added example of learning a program with multiple distinct head predicate symbols

Author: andrewcropper

examples/twoheads/bias.pl

@@ -0,0 +1,75 @@
+max_clauses(2).
+max_vars(5).
+max_body(6).
+
+%% trains
+head_pred(f1,1).
+body_pred(has_car,2).
+body_pred(has_load,2).
+body_pred(short,1).
+body_pred(long,1).
+body_pred(two_wheels,1).
+body_pred(three_wheels,1).
+body_pred(roof_open,1).
+body_pred(roof_closed,1).
+body_pred(zero_load,1).
+body_pred(one_load,1).
+body_pred(two_load,1).
+body_pred(three_load,1).
+body_pred(circle,1).
+body_pred(triangle,1).
+body_pred(rectangle,1).
+
+type(f1,(train,)).
+type(has_car,(train,car)).
+type(has_load,(car,load)).
+type(short,(car,)).
+type(long,(car,)).
+type(two_wheels,(car,)).
+type(three_wheels,(car,)).
+type(roof_open,(car,)).
+type(roof_closed,(car,)).
+type(zero_load,(load,)).
+type(one_load,(load,)).
+type(two_load,(load,)).
+type(three_load,(load,)).
+type(circle,(load,)).
+type(triangle,(load,)).
+type(rectangle,(load,)).
+
+direction(f1,(in,)).
+direction(has_car,(in,out)).
+direction(has_load,(in,out)).
+direction(short,(in,)).
+direction(long,(in,)).
+direction(two_wheels,(in,)).
+direction(three_wheels,(in,)).
+direction(roof_open,(in,)).
+direction(roof_closed,(in,)).
+direction(zero_load,(in,)).
+direction(one_load,(in,)).
+direction(two_load,(in,)).
+direction(three_load,(in,)).
+direction(circle,(in,)).
+direction(triangle,(in,)).
+direction(rectangle,(in,)).
+
+%% robots
+head_pred(f2,2).
+body_pred(up,2).
+body_pred(down,2).
+body_pred(left,2).
+body_pred(right,2).
+
+type(f2,(state,state)).
+type(up,(state,state)).
+type(down,(state,state)).
+type(left,(state,state)).
+type(right,(state,state)).
+
+direction(f2,(in,out)).
+direction(up,(in,out)).
+direction(down,(in,out)).
+direction(left,(in,out)).
+direction(right,(in,out)).
+