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( . functi , ) f (), (, ) X , , Υ. , . , X . f Υ, f : X → Υ → = f (), X. X . . f, {f()} f() [ f (X)] f. . ( ), (. ) , . . , . , , , , .

˳.: . . , . 1. ., 1970; . . , . 1. ., 1976; . . , . 1. ., 1981.

. . .