t1: no args
  x = <unset>
  y = <unset>
  z = <unset>
t1: some args
  x = 42
  y = <unset>
  z = `set'
t2: indirection
t1: via t2
  x = <unset>
  y = 6.283
  z = <unset>
t3: no args
  q = <unset>
  z = <unset>
t1: via t3
  x = 42
  y = <unset>
  z = <unset>
t3: x initially 19
  q = t
  z = `boing'
t1: via t3
  x = 20
  y = <unset>
  z = `boing'
t3 arg `q' present
t3 arg `z' present
t3 arg `nope' absent