DEFINITION I. If M is a space in which there is defined a metric dist (f, g) satisfying the usual postulates for distance ([1], p. 94), then a sequence F: fl, f2, * * * is fundamental if, for every 3>0, there exists an n = nli (3) such that m, n > ni imply dist (fn, f,) 0, there exists an n2 = n2(8) such that n > n2 implies dist (f, f,) < 8. M is complete if every fundamental sequence is convergent.