def C [b|c|d|f|g|h|k|l|m|n|p|q|r|s|t|v|w|x|z|%@];
def V [a|e|i|o|u];

def PhonWord [C* V (V) C*]+;

read lexc guesstest.lexc
substitute defined PhonWord for "^GUESSNOUNSTEM"

def Grammar;

def Phonology [..] -> e || [s h | c h | s | x | z] _ s .#. ;

def Grammar Grammar .o. Phonology ;

def GuessGrammar  $[ "+GUESS" ] .o. Grammar ;
def CleanGrammar ~$[ "+GUESS" ] .o. Grammar ;

regex CleanGrammar .p. GuessGrammar ;  # Lower-side priority union