It is useful to view computation as simulation, cf.: isomorphism of semigroups.[Preparata, F. P. and Yeh, R. T., Introduction to Discrete Structures, Addison-Wesley, 1973, p. 129.]
Given two semigroups G1 = [S, °] and G2 = [T, * ] , an invertible function &phi : S &rarr T is said to be an isomorphism between G1 and G2 if, for every a and b in S ,          &phi (a ° b) = &phi (a) * &phi (b)
from which:          a ° b = &phi -1 ( &phi (a) * &phi (b) )
(princ-to-string (+ (read-from-string "2") (read-from-string "3"))) "5"
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