:: deftheorem Def10 defines isotone FOMODEL4:def 10 :
for S being Language
for R being Rule of S holds
( R is isotone iff for Seqts1, Seqts2 being Subset of (S -sequents) st Seqts1 c= Seqts2 holds
R . Seqts1 c= R . Seqts2 );