- #1
Sajet
- 48
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Hi!
I have the following statements in a script on Riemannian submersions:
([itex]\pi[/itex] is the submersion [itex]\mathbb S^{2n+1} \rightarrow \mathbb{CP}^n[/itex] or [itex]\mathbb S^{4n+3} \rightarrow \mathbb{HP}^n[/itex] respectively.)
Regarding a) it is then said: "Let [itex]w \in T\mathbb{CP}^n, \lambda \in \mathbb C[/itex]. Let [itex]\bar w[/itex] be a horizontal lift of [itex]w[/itex]. Define [itex]\lambda w := \pi_*(\lambda \bar w)[/itex]. It is easily checked that this is well-defined."
I thought this was pretty clear. But then in b) they say:
"Let [itex]w \in T\mathbb{HP}^n[/itex], let [itex]\bar w[/itex] be a horizontal lift of w. Define [itex]w\mathbb H := \pi_*(\bar w\mathbb H)[/itex]. It is also easily checked that this is well-defined.
Warning: For [itex]\lambda \in \mathbb H[/itex] we cannot set [itex]w\lambda := \pi_*(\bar w\lambda)[/itex] as this is not well-defined."
Now I don't see why exactly the last part is not well-defined. I thought the horizontal lift is unique, therefore [itex]\bar w \lambda[/itex] would be unique and [itex]\pi_*(\bar w\lambda)[/itex] as well.
Or maybe I just don't understand what well-defined means in either case, and why exactly this definition would be viable in a) but not in b).
I'd be very grateful if someone could help me understand this.
I have the following statements in a script on Riemannian submersions:
a) [itex]T_{\bar p}\mathbb{CP}^n[/itex] carries the structure of a complex vector space for any [itex]\bar p \in \mathbb{CP}^n[/itex].
b) We can associate [itex]0 \neq v \in T_{\bar p}\mathbb{HP}^n[/itex] with a four-dimensional subspace [itex]v\mathbb H \subset T_{\bar p}\mathbb{HP}^n[/itex].
([itex]\pi[/itex] is the submersion [itex]\mathbb S^{2n+1} \rightarrow \mathbb{CP}^n[/itex] or [itex]\mathbb S^{4n+3} \rightarrow \mathbb{HP}^n[/itex] respectively.)
Regarding a) it is then said: "Let [itex]w \in T\mathbb{CP}^n, \lambda \in \mathbb C[/itex]. Let [itex]\bar w[/itex] be a horizontal lift of [itex]w[/itex]. Define [itex]\lambda w := \pi_*(\lambda \bar w)[/itex]. It is easily checked that this is well-defined."
I thought this was pretty clear. But then in b) they say:
"Let [itex]w \in T\mathbb{HP}^n[/itex], let [itex]\bar w[/itex] be a horizontal lift of w. Define [itex]w\mathbb H := \pi_*(\bar w\mathbb H)[/itex]. It is also easily checked that this is well-defined.
Warning: For [itex]\lambda \in \mathbb H[/itex] we cannot set [itex]w\lambda := \pi_*(\bar w\lambda)[/itex] as this is not well-defined."
Now I don't see why exactly the last part is not well-defined. I thought the horizontal lift is unique, therefore [itex]\bar w \lambda[/itex] would be unique and [itex]\pi_*(\bar w\lambda)[/itex] as well.
Or maybe I just don't understand what well-defined means in either case, and why exactly this definition would be viable in a) but not in b).
I'd be very grateful if someone could help me understand this.