Labour Leadership 2016

Here's an article on the claim: http://www.theargus.co.uk/news/14658211.Jeremy_Corbyn_rules_out_progressive_pact_with_Caroline_Lucas_in_Brighton/

What he actually says is a little bit less concrete:

But Mr Corbyn appeared to rule out any policy when speaking exclusively with The Argus.

He said: “At the moment no. What we are doing as a party committed to the Labour cause and position, in opposition in parliament in order to maximise votes against the government obviously we cooperate with other opposition parties.

“Does this translate into electoral pacts? No.”

I.e., it does not translate to electoral pacts, nor does it exclude them.