# Strong integral

An integral of Lebesgue type, either of a function with values in a linear topological space with respect to a scalar-valued measure, or of a scalar-valued function with respect to a vector-valued measure. Here, the limit processes by which the integral is defined are taken in the sense of the strong topology. Examples of strong integrals are:

1) The Bochner integral of a vector-valued function.

2) The Daniell integral, if the values of the integrand belong to a $\sigma$-complete vector lattice.

3) The integral $\displaystyle \int_{- \infty}^{\infty} \lambda ~ \mathrm{d}{F_{\lambda}}$, giving the spectral decomposition of a self-adjoint operator acting on a Hilbert space.

For the strong integral of scalar-valued functions with respect to a vector-valued measure, the values of the measure, in many cases, are assumed to belong to a semi-ordered vector space.

#### References

 [1a] N. Dunford and J.T. Schwartz, “Linear operators. General theory”, 1, Interscience (1958). [1b] N. Dunford and J.T. Schwartz, “Linear operators. Spectral theory”, 2, Interscience (1963). [2] T.H. Hildebrandt, “Integration in abstract spaces”, Bull. Amer. Math. Soc., 59 (1953), pp. 111–139.