ca632cca13
We can declare variables anywhere. So, we must also be able do declare
"universe" variables anywhere. Here is a minimal example that requires
this feature
```
-- We want A and B to be in the same universe
universe variable l
variable A : Type.{l}
variable B : Type.{l}
definition tst := A = B
```
The following doesn't work because A and B are in different universes
```
variable A : Type
variable B : Type
definition tst := A = B
```
The following works, but tst is not universe polymorphic, since l is
one *fixed* global universe
```
universe l
variable A : Type.{l}
variable B : Type.{l}
definition tst := A = B
```
28 lines
427 B
Text
28 lines
427 B
Text
import logic
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set_option pp.universes true
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universe u
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variable A : Type.{u}
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definition id1 (a : A) : A := a
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check @id1
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variable B : Type
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definition id2 (a : B) : B := a
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check @id2
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universe variable k
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variable C : Type.{k}
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definition id3 (a : C) := a
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check @id3
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universe variables l m
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variable A₁ : Type.{l}
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variable A₂ : Type.{l}
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definition foo (a₁ : A₁) (a₂ : A₂) := a₁ == a₂
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check @foo
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check Type.{m}
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