Control File: inconsistent architecture specification

When specifying architectures, they all need to be positive (as is) or negative (preceeded by the exclamation mark (!) character.) If there is any disparity, then this error occurs.

VALIDDepends: boost, qt [!ppc !alpha], libtld [i386 amd64]
INVALIDDepends: boost, qt [ppc !alpha], libtld [!i386 amd64]