<START> ::= if (<BOOL>) { <ACT> } else { <ACT> }
<ACT> ::= <START>|move_left();|move_right();|move_forward();|move_backward();
<BOOL> ::= greater_than(<VAR>,<VAR>)|smaller_than(<VAR>,<VAR>)|<VAR> == <VAR>|greater_than(<DIGIT>,<VAR>)|smaller_than(<DIGIT>,<VAR>)
<VAR> ::= wall_forward|wall_left|wall_right|wall_backward
<DIGIT> ::=0|1|2|3|4|5|6|7|8|9|<DIGIT><DIGIT>