no. 2
Non-archimedean invariant means
Compositio Mathematica, Tome 30 (1975) no. 2, pp. 169-180. 
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Schikhof, W. H. Non-archimedean invariant means. Compositio Mathematica, Tome 30 (1975) no. 2, pp. 169-180. http://archive.numdam.org/item/CM_1975__30_2_169_0/

[1] E. Hewitt and K.A. Ross: Abstract harmonic analysis I. Springer-Verlag, 1963. | Zbl

[2] A.C.M. Van Rooij: Non-archimedean functional analysis. Department of Mathematics, Catholic University, Nijmegen, The Netherlands, 1973.

[3] W.H. Schikhof: Non-archimedean harmonic analysis (Thesis). Nijmegen, 1967. | Zbl

[4] A.F. Monna: Analyse non-archimédienne. Springer-Verlag, 1970. | MR | Zbl

[5] A.C.M. Van Rooij: Invariant means with values in a non-archimedean field. Proc. Kon. Ned. Akad. v. Wetensch. 70 (1967) 220-228. | Zbl