  This paper updates the previous version in the following ways: 1. The main
result is extended from the case of sequence spaces to the case of Dedekind
complete Banach lattices. 2. A new appendix is added to mention some sufficient
and necessary conditions (which are probably already known) for lattices to be
Dedekind complete.
  We deal with the question of whether or not the p-convexified couple
(X_0^{(p)},X_1^{(p)}) is a Calderon couple under the assumption that (X_0,X_1)
is a Calderon couple of Banach lattices on some measure space. We find that the
answer is affirmative, not only in the case of sequence spaces treated in the
previous version, but also in the case where X_0 and X_1 are Dedekind complete
Banach lattices (and provided the same additional "positivity" assumption is
imposed regarding (X_0,X_1)). We also prove a quantitative version of the
result with appropriate norm estimates.
