(x_ {1}, t_ {1}), \ ldots, (x_ {n}, t_ {n})

(x_ {1}, t_ {1}), \ ldots, (x_ {n}, t_ {n})

(x_ {1}, t_ {1}), \ ldots, (x_ {n}, t_ {n})

(x_ {1}, t_ {1}), \ ldots, (x_ {n}, t_ {n})