Published online by Cambridge University Press: 13 September 2021
We prove two general results about the preservation of extendible and  $C^{(n)}$-extendible cardinals under a wide class of forcing iterations (Theorems 5.4 and 7.5). As applications we give new proofs of the preservation of Vopěnka’s Principle and
$C^{(n)}$-extendible cardinals under a wide class of forcing iterations (Theorems 5.4 and 7.5). As applications we give new proofs of the preservation of Vopěnka’s Principle and  $C^{(n)}$-extendible cardinals under Jensen’s iteration for forcing the GCH [17], previously obtained in [8, 27], respectively. We prove that
$C^{(n)}$-extendible cardinals under Jensen’s iteration for forcing the GCH [17], previously obtained in [8, 27], respectively. We prove that  $C^{(n)}$-extendible cardinals are preserved by forcing with standard Easton-support iterations for any possible
$C^{(n)}$-extendible cardinals are preserved by forcing with standard Easton-support iterations for any possible  $\Delta _2$-definable behaviour of the power-set function on regular cardinals. We show that one can force proper class-many disagreements between the universe and HOD with respect to the calculation of successors of regular cardinals, while preserving
$\Delta _2$-definable behaviour of the power-set function on regular cardinals. We show that one can force proper class-many disagreements between the universe and HOD with respect to the calculation of successors of regular cardinals, while preserving  $C^{(n)}$-extendible cardinals. We also show, assuming the GCH, that the class forcing iteration of Cummings–Foreman–Magidor for forcing
$C^{(n)}$-extendible cardinals. We also show, assuming the GCH, that the class forcing iteration of Cummings–Foreman–Magidor for forcing  $\diamondsuit _{\kappa ^+}^+$ at every
$\diamondsuit _{\kappa ^+}^+$ at every  $\kappa $ [10] preserves
$\kappa $ [10] preserves  $C^{(n)}$-extendible cardinals. We give an optimal result on the consistency of weak square principles and
$C^{(n)}$-extendible cardinals. We give an optimal result on the consistency of weak square principles and  $C^{(n)}$-extendible cardinals. In the last section prove another preservation result for
$C^{(n)}$-extendible cardinals. In the last section prove another preservation result for  $C^{(n)}$-extendible cardinals under very general (not necessarily definable or weakly homogeneous) class forcing iterations. As applications we prove the consistency of
$C^{(n)}$-extendible cardinals under very general (not necessarily definable or weakly homogeneous) class forcing iterations. As applications we prove the consistency of  $C^{(n)}$-extendible cardinals with
$C^{(n)}$-extendible cardinals with  $\mathrm {{V}}=\mathrm {{HOD}}$, and also with
$\mathrm {{V}}=\mathrm {{HOD}}$, and also with  $\mathrm {GA}$ (the Ground Axiom) plus
$\mathrm {GA}$ (the Ground Axiom) plus  $\mathrm {V}\neq \mathrm {HOD}$, the latter being a strengthening of a result from [14].
$\mathrm {V}\neq \mathrm {HOD}$, the latter being a strengthening of a result from [14].
 ${\omega}_1$
-strongly compact cardinals, this Journal, vol. 79 (2014), no. 1, pp. 266–278.Google Scholar
${\omega}_1$
-strongly compact cardinals, this Journal, vol. 79 (2014), no. 1, pp. 266–278.Google Scholar $\,\ne\,$
HOD
. 
Proceedings of the American Mathematical Society
, vol. 136 (2008), no. 8, pp. 2943–2949.CrossRefGoogle Scholar
$\,\ne\,$
HOD
. 
Proceedings of the American Mathematical Society
, vol. 136 (2008), no. 8, pp. 2943–2949.CrossRefGoogle Scholar $\kappa$
indestructible under
$\kappa$
indestructible under 
 $\kappa$
-directed closed forcing
. 
Israel Journal of Mathematics
, vol. 29 (1978), no. 4, pp. 385–388.CrossRefGoogle Scholar
$\kappa$
-directed closed forcing
. 
Israel Journal of Mathematics
, vol. 29 (1978), no. 4, pp. 385–388.CrossRefGoogle Scholar ${C}^{(n)}$
-extendible cardinals, this Journal, vol. 83 (2018), pp. 1112–1131.Google Scholar
${C}^{(n)}$
-extendible cardinals, this Journal, vol. 83 (2018), pp. 1112–1131.Google Scholar