  Subexponential logic is a variant of linear logic with a family of
exponential connectives--called subexponentials--that are indexed and arranged
in a pre-order. Each subexponential has or lacks associated structural
properties of weakening and contraction. We show that classical propositional
multiplicative linear logic extended with one unrestricted and two incomparable
linear subexponentials can encode the halting problem for two register Minsky
machines, and is hence undecidable.
