/* iGASM example */
/* Using main rules */
UNIVERSES U;
FUNCTIONS str : String;
FINAL U("");
RULES
IF str=undef THEN
  str := readln("Enter an element");
ELSEIF U(str) THEN
  CHOOSE s FROM U WHERE s=str WITH
    REMOVE s FROM U;
  ENDCHOOSE
  str := undef;
ELSE
  EXTEND U WITH str WITH
  ENDEXTEND
  str := undef;
ENDIF