:: deftheorem Def11 defines isotone FOMODEL4:def 11 :
for S being Language
for D being RuleSet of S holds
( D is isotone iff for Seqts1, Seqts2 being Subset of (S -sequents)
for f being Function st Seqts1 c= Seqts2 & f in D holds
ex g being Function st
( g in D & f . Seqts1 c= g . Seqts2 ) );