This category deals with topics in perturbation theory and variational principles, which commonly occur in the theory of differential equations, with problems in quantum mechanics forming an important subset thereof.
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- bat_smg
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- be_x_old
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- chy
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- crh
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- cu
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- cy
- da
- de
- diq
- dsb
- dv
- dz
- ee
- el
- eml
- en
- eo
- es
- et
- eu
- ext
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- ff
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- fiu_vro
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- frp
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- fy
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- gan
- gd
- gl
- glk
- gn
- got
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- gv
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- ii
- ik
- ilo
- io
- is
- it
- iu
- ja
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- kg
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- kj
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- km
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- kv
- kw
- ky
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- lad
- lb
- lbe
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- lij
- lmo
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- map_bms
- mdf
- mg
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- mk
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- mr
- mt
- mus
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- myv
- mzn
- na
- nah
- nap
- nds
- nds_nl
- ne
- new
- ng
- nl
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- no
- nov
- nrm
- nv
- ny
- oc
- om
- or
- os
- pa
- pag
- pam
- pap
- pdc
- pi
- pih
- pl
- pms
- ps
- pt
- qu
- quality
- rm
- rmy
- rn
- ro
- roa_rup
- roa_tara
- ru
- rw
- sa
- sah
- sc
- scn
- sco
- sd
- se
- sg
- sh
- si
- simple
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- sl
- sm
- sn
- so
- sr
- srn
- ss
- st
- stq
- su
- sv
- sw
- szl
- ta
- te
- tet
- tg
- th
- ti
- tk
- tl
- tlh
- tn
- to
- tpi
- tr
- ts
- tt
- tum
- tw
- ty
- udm
- ug
- uk
- ur
- uz
- ve
- vec
- vi
- vls
- vo
- wa
- war
- wo
- wuu
- xal
- xh
- yi
- yo
- za
- zea
- zh
- zh_classical
- zh_min_nan
- zh_yue
- zu
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