Bohrs principle of complementarity, in the context of a two-slit interference experiment, is understood as the quantitative measures of wave and particle natures following a duality relation ${mathcal D}^2+{mathcal V}^2 le 1$. Here ${mathcal D}$ is a measure of distinguishability of the two paths, and ${mathcal V}$ is the visibility of interference. It is shown that such a relation can be formulated for $N-$slit or $N-$path interference too, with the proviso that the wave nature is characterized by a measure of {em coherence} (${mathcal C}$). This new relation, ${mathcal D}^2+{mathcal C}^2 le 1$ is shown to be tight, and reduces to the known duality relation for the case $N=2$. A recently introduced similar relation (Bagan et al., 2016) is shown to be inadequate for the purpose.
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