1 (universal algebra) . ? . , . , ( ) , , , , . “ ” , ( ). , 1 , ( ) . . , , . , . , . , 𝐴 𝐴 . , . , ( ). ? , . . . , , , . , , Birkhoff (1935) . , . , . , , , , . , (Lawvere , ) . , , Birkhoff . , . RPG . , “ ” . 1 , [3, 2, 4, 1] , [1] . , ( variety , subdirect product ). , . 2.5 . , . 2 ? 𝑋 . 𝑋 (operation) , 𝑓 Ȃ 𝑋𝑛 Ă 𝑋 (𝑛 Ȃ 0) . 𝑛 𝑓 (arity) . 𝑛 = 0 𝑓 . , 𝐴 𝐴 . 𝐀 = 𝐴܂, {𝑓𝑖}𝑖