Is Bitcoin the first e-cash scheme which solved the double-spend problem?
Yes. Bitcoin is the first trustless e-cash protocol, which solves the double-spend problem. If anyone else needs an academic source to back up this claim, there is at least this one:

Brito, Jerry ja Castillo, Andrea: Bitcoin: A primer for policymakers.
Mercatus Center at George Mason University, 2013

https://www.mercatus.org/publication/bitcoin-primer-policymakers