Schreinemakers theorem of coincidence

Consider cf s phases which form an indifferent subsystem. The monovariant curves of all the parent systems containing these f s phases in the same state, when projected on the (T, p) plane, have a common tangent at the point corresponding to this state. 

This follows immediately since all the projections of mono variant lines must, because of the theorem proved in 17, be tangents at the same point to the same lines of indifference, corresponding to the common sub-system. 

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