npm install --save @angular/material

import { MaterialModule } from '@angular/material';

ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-item.d.ts:14:27
';' expected.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-item.d.ts:14:29
Duplicate identifier 'string'.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-item.d.ts:15:4
Duplicate identifier 'readonly'.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-item.d.ts:15:13
'=' expected.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-item.d.ts:15:13
Cannot find name '_tabindex'.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-item.d.ts:15:22
';' expected.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-item.d.ts:15:24
Duplicate identifier 'string'.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-trigger.d.ts:26:4
Duplicate identifier 'readonly'.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-trigger.d.ts:26:13
'=' expected.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-trigger.d.ts:26:13
Cannot find name 'menuOpen'.
ERROR in [default] C:/mypathSource/Repos/dir/Web.Angular/node_modules/@angular/material/menu/menu-trigger.d.ts:26:21
';' expected.

@NgModule({
  imports: [
    ...
    MaterialModule.forRoot(),
    ...
  ]
  ...
})