thmtools conflicts with LLNCS template causes environment prop undefined and also already defined error

[HaoSun1]

LLNCS conflicts with thmtools, in particular with thm-restate. This causes an error where prop is both undefined and when you try to define it it tells you it's already defined.

there is a bug in how thmtools is trying to latch onto the LLNCS macros and provide its own interpretation of stuff.
Willie Wong has been able to isolate the bug to the file thm-llncs.sty; the specific error is coming from the call to \thmt@newtheorem@predefinition in the definition of \thmt@spnewtheoremiv. See rest of post here.

https://tex.stackexchange.com/questions/699875/environment-prop-undefined-and-also-already-defined-lncs-template