If two geometries are parallel they have the same orientation. euclid allows
assessing parallelity of a broad range of geometries. If `x`

and `y`

are
surfaces the parallelity of their supporting plane is returned. If `x`

and
`y`

are curves, the parallelity of their supporting line is returned. If it
is a mix of surface and curve, the parallelity is calculated as whether the
supporting plane and supporting line intersects at a point.

`parallel(x, y)`

- x, y
vectors of geometries

a logical vector giving the parallelity of the input

Other Predicates:
`collinear()`

,
`constant_in`

,
`geometry_class`

,
`geometry_turns`

,
`has_intersection()`

,
`in_order()`

,
`is_degenerate()`

,
`location_predicates`

```
# Are two triangles parallel (only meaningful in 3D)
p <- point(sample(20, 6), sample(20, 6), sample(20, 6))
t1 <- triangle(p[1], p[2], p[3])
t2 <- triangle(p[4], p[5], p[6])
parallel(t1, t2)
#> [1] FALSE
# Same as:
parallel(as_plane(t1), as_plane(t2))
#> [1] FALSE
# Parallelity of surface and curve
parallel(t1, line(p[5], p[6]))
#> [1] FALSE
```