ROOTS

Imported a theorem about Infinite_Sum. Importing this theory a bit earlier is causing syntactic ambiguities with Infinite_Set_Sum however; no_notation needed

src/Pure
src/FOL
src/HOL
src/ZF
src/CCL
src/CTT
src/Cube
src/FOLP
src/LCF
src/Sequents
src/Doc
src/Tools