seq vs array vs open array

[cblake]

FWIW, @dlesnoff \- if you don't mind getting a `seq` as a result then you could 
also just use `system.@` and `system.&`:
    
    
    const x = [1,2]
    const y = [3,4,5]
    const z = @x & @y
    echo z
    echo type(z)
    
    
    Run

This is mentioned in @kaushalmodi's notes.