A fuzzy conjunction operators, t(x, y), and a fuzzy disjunction operator, s(x, y), form a pair if they satisfy:
t(x, y) = 1 – s(1 – x, 1 - y).
If \(t\left( {x,\;y} \right) = \frac{{xy}}{{\left( {x + y - xy} \right)}}\) then s(x, y) is given by1
\(\frac{{x\; + \;y}}{{1\; -\; xy}}\)
2
\(\frac{{x\; + \;y\; - \;2xy}}{{1\; - \;xy}}\)
3
\(\frac{{x\; + \;y\; - \;xy}}{{1\; - \;xy}}\)
4
\(\frac{{x\; + \;y\; - \;xy}}{{1\; + \;xy}}\)