ratiocinator
Lightly seared on the reality grill.
I can have a concept that is the concept of a group of concepts.No a concept is a singleton.
Okay.Please precisely describe the conceptual difference between LI and {LI}?
It's easier to see from the finite examples but LI has some sort of infinite cardinality because it contains an infinite number of concepts, {LI} has a cardinality of 1 because it contains just one element. That element is LI.
A finite example is P = {1, 2, 3}, Q = {4, 5}. Q has cardinality 2 but {Q} = {{4, 5}} has cardinality 1.
Now P ∪ Q = {1, 2, 3, 4, 5} (cardinality 5), but P ∪ {Q} = {1, 2, 3, {4, 5}} (cardinality 4).
My signature asserts the existence of an infinite set, starting with just the empty set, ∅ = {}, using exactly this process.
We start with ∅ ∈ x, so the empty set is in x, but then we have ∀y ∈ x((y ∪ {y}) ∈ x).
So, if we work through building x, we start with ∅ ∈ x
so x = {∅, ...} = {{}, ...}
Then take ∀y ∈ x((y ∪ {y}) ∈ x), with y = ∅ from above,
∴ ∅ ∪ {∅} = {∅} = {{}} ∈ x,
∴ x = {∅, {∅}, ...} = {{}, {{}}, ...}
Now repeat with y = {∅}
∴ {∅} ∪ {{∅}} = {∅, {∅}} ∈ x
∴ x = {∅, {∅}, {∅, {∅}}, ...} = {{}, {{}}, {{}, {{}}}, ...}
...and so on.
Fun, eh?