:: deftheorem Def4 defines LF DIOPHAN2:def 5 :
for a0, b0, c0 being Real
for b₄ being Function of [:INT,INT:],REAL holds
( b₄ = LF (a0,b0,c0) iff for x, y being Integer holds b₄ . (x,y) = ((a0 * x) + (b0 * y)) + c0 );