error "undefined method `SymEngine' for main:Object" makes many notebook-examples fail

[dwarfi09]

A lot of the notebook-examples fail:

d = SymEngine(1.2)
undefined method `SymEngine' for main:Object

i = SymEngine::I
uninitialized constant SymEngine::I

i2 = SymEngine::cos(0.2)
undefined method `cos' for SymEngine:Module

SymEngine::nextprime(5)
undefined method `nextprime' for SymEngine:Module

and many more.

The first examples (like SymEngine::Symbol.new("x")) work.

I installed current symengine-version from github. I tried the symengine-gem version 0.0.2 with ruby 2.3.3 and ruby 2.6.5 - same failures with both versions.

Should this gem still work with current symengine?