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Object-oriented Programming in C#
Contracts and Assertions
Obligations and Benefits in Sqrt

sqrt(x: Real) -> Real

  precondition: x >= 0;

  postcondition: abs(result * result - x) <= 0.000001

An axiomatic specification of the squareroot function.

ClientMust pass a non-negative numberReceives the squareroot of the input
ServerReturns a number r for which r * r = xTake for granted that x is non-negative

A tabular presentation of the obligations and benefits of the squareroot function (in a server role) and its callers (in a client role).

Notice in particular the obligation of the client and the benefit of the server