Cannot use UFCS in lambda?

[Vladimir Panteleev]

On Sunday, 16 September 2018 at 09:46:15 UTC, berni wrote:
> Where is my mistake?

Lambdas are not the issue here. The problem is more general: you 
can only use top-level symbols in UFCS.

You can use an identity alias template to bypass this:
https://blog.thecybershadow.net/2015/04/28/the-amazing-template-that-does-nothing/
(search for UFCS in the page).