Sourcetype ('arg1, 'arg2, 'output) service2 =
((unit * 'arg1) * 'arg2, (Req.t * 'arg1) * 'arg2, unit, 'output) service Sourcetype ('arg, 'input, 'output) post_service1 =
(unit * 'arg, Req.t * 'arg, 'input, 'output) service Sourcetype ('arg1, 'arg2, 'input, 'output) post_service2 =
((unit * 'arg1) * 'arg2, (Req.t * 'arg1) * 'arg2, 'input, 'output) service