Here is a list of all documented namespace variables with links to the namespaces they belong to:

begin : halcheck::lib
element : halcheck::gen
element_of : halcheck::gen
empty : halcheck::lib
end : halcheck::lib
ignore : halcheck::lib
in_place : halcheck::lib
invoke : halcheck::lib
label : halcheck::gen
make_filter_iterator : halcheck::lib
make_index_iterator : halcheck::lib
make_iota_iterator : halcheck::lib
make_transform_iterator : halcheck::lib
nullopt : halcheck::lib
optional : halcheck::gen
range : halcheck::gen
sample : halcheck::gen
scale : halcheck::gen
size : halcheck::lib
transform : halcheck::lib