We deal with a conditional functional equation
ϕ(x) = ϕ(y) implies f(x+y) = f(x)+f(y).
Under some assumptions imposed on function ϕ, the domains and ranges of ϕ and f we derive the additivity of f. As a consequence we obtain two Hyers-Ulam stability results related to the equation considered.
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Vol. 11 (1997)
Published: 1997-09-30