Post by frrrstfnAccording to Oberon 07 report the symbol <= and >= denote set
inclusion.
My question is an empty SET always included in a non empty SET ?
Only if the set includes the empty set.
{} <= {{}}
Post by frrrstfne.g. : {} <= {0} is TRUE?
Inclusion is a relation between an element and a set.
Subset is a relation between two sets.
Some confusion may occur, because you may define set of sets
(mathematically), and a set may be an element of another set (of sets)
or a subset of another set.
I've not read the Oberon 07 report, so I don't know what terminology
it uses or how it defines <= and >= when one or both of the operands
are sets.
IIRC, in Modula-2, there were only sets of small integers, (so they
could be represented by a word of bits), and <= and => denoted the
subset ⊂ and superset ⊃ relations, not the element-of ∈, or contains ∋
relations.
So,
{} ⊂ {0} is true
{} ∈ {0} is false
{} <= {0} depends on the meaning of <=. Read the report again!
--
__Pascal Bourguignon__ http://www.informatimago.com/