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[tlaplus] Proving inductive predicates in TLAPS

I have a specification with constant Blocks and a function prev \in [Blocks -> Blocks] that defines a tree.
I would like to define an ancestor relation on that tree and prove statements like reflexivity and transitivity.

If I try to prove NatInductiveDefConclusion, it triggers a bug in TLAPS.
I would be grateful for any tips on how to define the ancestor relation, or how to avoid the bug.

Here is my current definition of the ancestor relation:
Extend(A) == A \cup { <<b,c>> \in Blocks \X Blocks: <<b,prev[c]>> \in A }
A0 == { <<b,c>> \in Blocks \X Blocks: b=c }

ancestors[i \in Nat] == IF i=0 THEN A0
                                        ELSE Extend(ancestors[i-1])

Ancestor(b,c) == /\ height[b] <= height[c]
                               /\ height[c] - height[b] \in Nat
                               /\ <<b,c>> \in ancestors[height[c] - height[b]]
My complete tree specification can be found here:



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